Centaurea maculosa and Centaurea stoebe (= rhenana) are rather similar knapweeds with narrow leaves
and an involucre which in bud is about as high as its diameter.
The bracts are greenish. At Centaurea maculosa the rather smooth surface of the bracts merges in the upper part
into a brown blunt end, while on the surface of the bracts of Centaurea stoebe considerable nerves can be seen
and the darker upper end is ending in a short tip.
According to 'Flora Europaea' volume 4 another difference is that Centaurea maculosa has often a dark spot
at the lower base of the bracts (therefore the name), while Centaurea stoebe doesn't have this.